Thermal inactivation kinetics of wheat germ lipoxygenase

Thermal inactivation curves for wheat germ lipoxygenase (LPO) in partially purified and crude extracts were determined in capillary tubes at 60–68°C. The biphasic curves fitted a two-fraction first order model suggesting the presence of 2 groups of isozymes. At 60°C, the inactivation rate constants were 9.112 × 10−-5 set−1 and 9.174 × 10−-6 set−1 respectively, for thermolabile phase I and thermostable phase II in the partially purified extract, a difference of one order of magnitude. For the temperature change from 60 to 68°C, the rate constants increased by three orders of magnitude, implying a very high sensitivity (for LPO inactivation in partially purified extract ΔH‡= 646261 J.mole−1, ΔS‡= 1619 J.mole−1.K−1 for phase I, ΔH‡= 546099 J.mole-l, ΔS‡= 1298 J.mole−1.K-1′ for phase II) to heat by both phases, although phase I was clearly the least stable.